In many situations, there is a need to provide an electrical connection to structures of various sized and shaped cross-sections for grounding purposes. The purpose of such a connection may be to ground electrical devices and interconnections through a connection to a cold water pipe or other suitable structure, or to ground pipes, conduit, and other structures of electrical and/or mechanical systems, in order to dissipate an electrical charge to protect such components and/or the individuals who may come into contact with these components. Grounding assemblies are commonly employed for these purposes.
Grounding assemblies come in a variety of configurations and use various means for electrically and mechanically attaching to a conductive structure. One type of assembly includes a metal strap with a plurality of holes, a metal stud, and conventional nuts to secure the strap about the periphery of the structure. More specifically, the strap encircles the structure and the stud is inserted through two of the holes to secure the strap tightly around the periphery of the conductive structure. The strap is drawn tightly around the periphery of the structure as the nuts are tightened on the stud.
The assembly typically includes a ground terminal to receive a wire for connecting the assembly to a conventional ground mechanism, such as a ground rod, or to allow the connection of a wire from an electrical device, interconnection, or system which requires grounding. In effecting such grounding, generally a ground wire is appropriately connected to a grounded structure (if the pipe or conduit must be grounded) or to a device, interconnection, or system (if the pipe or conduit will function as the grounded structure). The coupling between the ground wire to the pipe or conduit is done in a manner which ensures an effective electrical connection between the pipe or conduit and the ground wire. This coupling or connection is generally maintained free from corrosion and mechanical failure, both at the connection with the ground wire and the connection to the pipe or conduit, in order to ensure that the electrical connection therebetween is maintained.
Strap-type assemblies may accommodate different diameters of pipes or conduits, or cross-sections of differently shaped structures, such as ellipses, ovals, rectangles, and boxes. This adaptability of the strap-type assembly to a variety of conductive structures eliminates the need for an inventory of grounding assemblies that are specifically designed for a specific structure.
Strap-type assemblies generally use conventional hexagonal nuts having sharp edges to tighten the strap assembly to the conductive structure. The sharp edges of the nuts are known to gouge the metal strap as the strap is tightened at the stud. The gouging of the strap causes creases and areas of weakness which shorten the overall life of the strap and can limit the effectiveness with which it conducts electricity. The creases and/or areas of weakness may also cause the strap to break as the strap assembly is tightened around the conductive structure.
Generally, in order to install a strap-type assembly, the strap is tightened about the conductive structure to a predetermined torque to ensure that the strap is sufficiently secured to the structure, but without an excessive force being applied to the strap which could cause the strap to fail. The prior art utilization of hexagonal-shaped nuts has caused problems in this respect by making it difficult to apply the full torquing force to secure the strap onto the conductive structure. Since the curvature of the strap when attached to the conductive structure causes the strap to engage the threaded stud at an angle, the use of conventional nuts, which have an across-points dimension that is greater than the across-flats dimension of the nut, many times creates a false torque reading. Such a false reading occurs due to the manner in which the hexagonal nut engages the angled strap, whereby the larger across-points dimension causes the edges of the nut to engage the strap itself as the hexagonal nut is rotated. The contact between the hexagonal nut edge and the strap may gouge the strap, as discussed above, and requires an increased force to turn the hexagonal nut on the threaded stud, which can erroneously be interpreted as the force being applied by a torque wrench, or other torque-measuring device, between the strap and the conductive structure. Thus, such prior art devices not only damage the strap through gouging, but may also fail to sufficiently secure the strap to the conductive structure.
One solution to the problem of gouging, or otherwise providing a non-destructive tightening of the strap, is disclosed in U.S. Pat. No. 4,626,051, which issued to the same inventor as for the present invention. This patent discloses the use of two nuts, each having a curved surface for engaging the strap. The curvature of the surfaces better accepts the angle of the strap as it leaves the various structures and attaches to the stud and better distributes the force applied to the strap over a larger area. While this advancement addresses gouging of the strap by eliminating the sharp edges of engagement, at least one of the nuts must be removed from the stud during installation, and this leads to the possibility of losing the nut and/or lost time retrieving the displaced nut. This situation is compounded by the fact that many installations of strap assemblies are made in awkward and sometimes dangerous locations, such as those to suspended systems or pipes, requiring the installer to use scaffolding, catwalks, and/or ladders to reach the desired structure for attachment.
A solution to the issue of the detachment of one of the nuts is addressed in U.S. Pat. No. 6,559,387, which also issued to the same inventor as for the present invention. This patent discloses the use of a sliding nut captivated on the strap in place of one of the nuts. The sliding nut is captivated on the strap, such that the sliding nut remains secured to the strap during installation and need not be removed from the strap. However, several shortcomings remain unresolved despite this advance. Most notably, the hole for receiving the stud generally has a diameter that is larger than the diameter of the stud, such that the stud may fall out of the hole and be materially displaced or even lost prior to attachment to a conductive structure. Likewise, although the use of a captivated sliding nut is advantageous, the stud is still used to carry the second nut and can be unintentionally displaced from the assembly. Moreover, the use of a nut complicates the manufacturing of the strap assembly, since it is a separate component and must be threaded onto the stud during the manufacturing process, and also gives rise to the possibility that the nut could be lost if it is accidentally unthreaded from the stud during installation.